1. Field of the Invention
This invention relates to a radiation image recording and read-out apparatus for storing a radiation image on a recording belt coated with a stimulable phosphor layer, exposing the stimulable phosphor layer to stimulating rays which cause it to emit light in proportion to the stored image information and detecting the emitted light to obtain an electric image signal, and more particularly to a radiation image recording and read-out apparatus of such type wherein the stimulable phosphor layer is formed on an endless belt.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .tau.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in the applicant's U.S. Pat. No. 4,258,264 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor is first exposed to a radiation passing through an object to have a radiation image stored thereon, and is then two-dimensionally scanned with stimulating rays such as a laser beam which cause it to emit light in the pattern of the stored image. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image on a recording medium such as a photographic light-sensitive material or on a display device such as a cathode ray tube (CRT).
The radiation image recording and reproducing system using a stimulable phosphor sheet is advantageous over conventional radiography using a silver halide photographic material in that the image can be recorded over a very wide range (latitude) of radiation exposure. More specifically, since the amount of light emitted upon stimulation after the radiation energy is stored on the stimulable phosphor varies over a very wide range in proportion to the amount of energy stored thereon, it is possible to obtain an image having desirable density regardless of the amount of exposure of the stimulable phosphor to the radiation, by reading out the emitted light with an appropriate read-out gain and converting it to an electric image signal to reproduce a visible image on a recording medium or a display device such as a CRT.
In this radiation image recording and reproducing system, the stimulable phosphor sheet is used only for temporarily storing the radiation image in order to reproduce the final visible image therefrom on a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheets be used repeatedly.
In view of this, the applicant developed a radiation image recording and reproducing system which enables stimulable phosphor sheets to be circulated and reused with high efficiency. As described in, for example, U.S. Pat. No. 4,543,479, this earlier proposed system integrally comprises: a support; a stimulable phosphor sheet consisting of a layer of a stimulable phosphor capable of storing a radiation image fixed on the support; an image recording section for recording a radiation transmission image of an object on the stimulable phosphor sheet by exposing the stimulable phosphor sheet to a radiation passing through the object; an image read-out section consisting of a stimulating ray source for emitting stimulating rays for scanning the stimulable phosphor sheet carrying the radiation image stored thereon in the image recording section, and a photoelectric read-out means for detecting light emitted from the stimulable phosphor sheet scanned with the stimulating rays to obtain an electric image signal; a circulation and conveyance means for repeatedly moving the support and the image read-out relative to each other so as to cause the stimulable phosphor sheet to be repeatedly circulated relative to the image read-out section; and an erasing section for, prior to the next image recording on the stimulable phosphor sheet for which the image read-out has been conducted in the image read-out section, exposing the stimulable phosphor sheet to erasing light to release the radiation energy remaining on said stimulable phosphor sheet; whereby the stimulable phosphor sheet is efficiently circulated and reused.
In this system, it is highly convenient to form the stimulable phosphor sheet as an endless recording belt consisting of an endless belt coated with a stimulable phosphor layer since this allows the recording belt to be supported on rollers or the like and conveyed successively through the image recording section, the image read-out section and the erasing section.
Among radiation image recording and read-out apparatuses utilizing a recording belt formed as an endless support belt coated with a stimulable phosphor layer, that proposed by the applicant in U.S. patent application Ser. No. 143,919 now U.S. Pat. No. 4,847,499 is of particular interest for its compact size and the high degree of precision with which it enables the scanning with stimulating rays to be carried out. In this recording and read-out apparatus the endless support belt is carried on two roller sections each comprising a pair of rollers. The roller sections are separated by a distance approximately equal to the length of a single radiation image and the image recording section is disposed so as to carry out image recording on the recording belt between the two roller sections. This makes it possible to hold one dimension of the apparatus to approximately the length of a single image. Moreover, the scanning of the recording belt with stimulating rays is carried out at the position where the recording belt passes over one of the rollers. This being the position at which the recording belt travels most stably, the scanning with the stimulating rays can thus be carried out with high precision unaffected by undulation etc. of the recording belt.
However, while the aforesaid recording and read-out apparatus using an endless recording belt is advantageous in that it facilitates the circulation of the stimulable phosphorus layer, it has the drawback that the recording belt is apt to travel in a snaking fashion during operation of the apparatus. While snaking of the recording belt of course makes high-precision image read-out impossible, it may also cause the recording belt to ride up on the side plates and incur irreparable damage.